Czech painter František Kupka (1871-1957), who spent his active years in Paris, remains one of the most under-researched artists, given his important status as one of the first painters of totally abstract works of art, beginning in 1912. As such, his philosophical and iconographical sources have yet to be fully discussed. This thesis examines how three of Kupka's sources, Buddhism, Theosophy, and science, demonstrate his belief in the existence of an immaterial reality, which shaped his art and theory. In the late nineteenth and early twentieth centuries, the notion of invisible realities was a widespread concern of individuals aware of science and/or interested in mysticism and occultism. In this context, Buddhism would have offered another model for new ways of envisioning existence and consciousness. Two of Kupka's early works, The Soul of the Lotus (1898) and The Beginning of Life (1900), show his knowledge of Buddhist, and possibly Hindu, iconography. The Musée Guimet in Paris offered a rich supply of material by which an individual could learn about Buddhism, and Kupka's imagery likely drew upon such sources. In addition to the Musée Guimet, it is likely Kupka also encountered Buddhism through popularized Eastern thought--in part through books published in Paris on that subject as well as on Theosophy. The writings of Theosophical authors regularly addressed themes related both to Buddhism and to contemporary science, which was equally concerned with the invisible and the immaterial. Discoveries such as the X-ray, for example, affirmed the inaccuracy of human vision and the existence of a reality beneath surface appearances, which supported Theosophy in its reaction against materialism. I argue that Kupka's 1909 painting The Dream serves as a culmination of his concern for alternative conceptions of reality. Painted using a formal language of transparency, The Dream demonstrates Kupka's interest in Buddhism, Theosophy, and science and represents his belief in the immaterial as a critical stage in his philosophical and artistic evolution.